CN111584602A

CN111584602A - Display substrate, preparation method thereof and display device

Info

Publication number: CN111584602A
Application number: CN202010465178.9A
Authority: CN
Inventors: 田雪雁; 朱健超; 杨艳艳; 陈登云; 黄硕; 秦成杰
Original assignee: BOE Technology Group Co Ltd
Current assignee: BOE Technology Group Co Ltd
Priority date: 2020-05-28
Filing date: 2020-05-28
Publication date: 2020-08-25
Anticipated expiration: 2040-05-28
Also published as: WO2021238465A1; CN111584602B; US20220285653A1

Abstract

The disclosure provides a display substrate, a preparation method thereof and a display device. The display substrate includes: the light-emitting diode comprises a substrate, a light-emitting structure layer positioned on the substrate, an encapsulation structure layer positioned on the light-emitting structure layer, a reflecting layer positioned on the encapsulation structure layer, a hydrophilic material layer positioned on the reflecting layer and an optical adhesive layer positioned on the hydrophilic material layer. According to the display substrate, the hydrophilic material layer is arranged on one side, away from the substrate base plate, of the reflection layer, the optical adhesive layer is attached to the surface of the hydrophilic material layer, and compared with the case that the optical adhesive layer is directly attached to the reflection layer, the hydrophilic material layer can improve the adhesive force of the optical adhesive layer on the surface of the hydrophilic material layer, and the defects that bubbles are generated between the interface of the optical adhesive layer and the interface of the hydrophilic material layer, the optical adhesive layer is separated from the hydrophilic material layer and the like; the hydrophilic material layer can play the guard action to the reflector layer, avoids laminating the damage reflector layer of optical cement in-process, has promoted rear end module laminating and reliability yield by a wide margin.

Description

Display substrate, preparation method thereof and display device

Technical Field

The disclosure relates to the technical field of display, in particular to a display substrate, a preparation method thereof and a display device.

Background

Organic Light Emitting Diode (OLED) display substrates are widely used in the display fields of mobile phones, tablet computers, digital cameras, etc. due to their advantages of low energy consumption, low production cost, self-luminescence, wide viewing angle, fast response speed, etc.

With the rapid development of display technologies, various emerging technologies are emerging, and display devices with multiple functions have become one of the goals pursued by people. At present, the mirror display device appearing in the market is widely used because the display function and the mirror function can be simultaneously realized. The mirror surface display means that a user can see a display picture from a display of the mirror while using the mirror, so that various requirements of people are met, such as an advertisement display screen in a public place, a vehicle-mounted rearview mirror, a display screen of an ATM (automatic teller machine), and the like.

In the prior art, the OLED mirror display screen adopts a reflective layer to reflect light to function as a mirror. An Optical Clear Adhesive (OCA) layer is attached to the upper side of the reflective layer. In the process of bonding the optical adhesive layer, when poor bonding and pressing occur, the reflecting layer can be damaged, or defects such as bubbles and separation can be generated, so that the product reliability yield is reduced.

Disclosure of Invention

An object of the present disclosure is to provide a display substrate, a method for manufacturing the same, and a display device, so as to solve the problem of poor adhesion of an optical adhesive layer.

In order to solve the above technical problem, an embodiment of the present disclosure provides a display substrate, including:

a substrate base plate;

the light emitting structure layer is positioned on one side of the substrate and comprises a plurality of light emitting units;

the packaging structure layer is positioned on one side of the light emitting structure layer, which is far away from the substrate;

the reflecting layer is positioned on one side of the packaging structure layer, which is far away from the substrate base plate;

the hydrophilic material layer is positioned on one side of the reflecting layer, which is far away from the substrate base plate;

and the optical adhesive layer is positioned on one side of the hydrophilic material layer, which deviates from the substrate base plate.

In some possible implementations, the material of the hydrophilic material layer includes a silicon-based super-hydrophilic oxide, or the material of the hydrophilic material layer includes an organic colloid having hydrophilicity.

In some possible implementations, the hydrophilic material layer has a thickness of 1200 to 1700 angstroms.

In some possible implementation manners, the display substrate includes a display area, a frame area located at the periphery of the display area, and a bonding area, the hydrophilic material layer is located in the display area, the frame area, and the bonding area, and the hydrophilic material layer is provided with a second exposure hole located in the bonding area and used for exposing a bonding pad of the bonding area.

In some possible implementations, the orthographic projection of the hydrophilic material layer on the substrate base plate includes the orthographic projection of the reflective layer on the substrate base plate, and the orthographic projection of the reflective layer on the substrate base plate includes the orthographic projection of the encapsulation structure layer on the substrate base plate.

In some possible implementation manners, the reflective layer is located in the display area, the frame area and the bonding area, the reflective layer is provided with light holes located in the display area and corresponding to the light emitting units one by one, and the reflective layer is further provided with first exposure holes located in the bonding area and used for exposing bonding pads of the bonding area.

In some possible implementations, the material of the reflective layer includes one or more of the following materials: molybdenum, aluminum, silver, titanium, indium tin oxide/silver/indium tin oxide multilayer composite material, titanium/aluminum/titanium multilayer composite material.

In some possible implementations, the reflective layer has a thickness of 0.25 μm to 0.4 μm.

In some possible implementations, the display substrate further includes a protective layer located between the encapsulation structure layer and the reflective layer, and the material of the protective layer includes at least one of the following materials: silicon nitride, silicon oxide, and a silicon nitride/silicon oxide composite layer.

In some possible implementations, the protective layer has a thickness of 0.2 μm to 0.4 μm.

In some possible implementations, the orthographic projection of the protection layer on the substrate includes the orthographic projection of the package structure layer on the substrate.

In some possible implementation manners, the encapsulation structure layer includes a first inorganic encapsulation layer, an organic encapsulation layer, and a second inorganic encapsulation layer, which are sequentially stacked on a side of the light emitting structure layer away from the substrate.

In some possible implementation manners, the substrate includes a base structure layer and a driving structure layer located on a side of the base structure layer facing the light emitting structure layer, the base structure layer includes a first base, a second base, a third base and a buffer layer, which are sequentially stacked, the driving structure layer is located on a side of the buffer layer facing away from the first base, and each of the first base, the second base and the third base includes at least one of the following materials: pressure sensitive adhesive, polyimide, polyethylene terephthalate, and surface-treated polymer film.

In order to solve the above technical problem, an embodiment of the present disclosure further provides a display device including the display substrate described above.

In order to solve the above technical problem, an embodiment of the present disclosure further provides a method for manufacturing a display substrate, including:

forming a light emitting structure layer on one side of a substrate, the light emitting structure layer including a plurality of light emitting cells;

forming a packaging structure layer on one side of the light emitting structure layer, which is far away from the substrate;

forming a reflecting layer on one side of the packaging structure layer, which is far away from the substrate;

forming a hydrophilic material layer on one side of the reflecting layer, which is far away from the substrate base plate;

and an optical adhesive layer is attached to one side of the hydrophilic material layer, which is far away from the substrate base plate.

In some possible implementations, the display substrate includes a display area, a frame area located at a periphery of the display area, and a binding area, and a hydrophilic material layer is formed on a side of the reflective layer facing away from the substrate, including:

forming a hydrophilic material film positioned in a display area, a frame area and a binding area on one side of the reflecting layer, which is far away from the substrate;

and patterning the hydrophilic material film through a patterning process to form a hydrophilic material layer, wherein the hydrophilic material layer is provided with a second exposure hole which is positioned in the binding area and used for exposing the binding welding pad of the binding area.

According to the display substrate, the hydrophilic material layer is arranged on the side, away from the substrate, of the reflection layer, and the optical adhesive layer is attached to the surface of the hydrophilic material layer, so that compared with the case that the optical adhesive layer is directly attached to the reflection layer, the hydrophilic material layer can improve the adhesion of the optical adhesive layer to the surface of the hydrophilic material layer, and the defects that bubbles are generated between the interface of the optical adhesive layer and the interface of the hydrophilic material layer, the optical adhesive layer is separated from the hydrophilic material layer and the like are avoided; in addition, the hydrophilic material layer can play the guard action to the reflecting layer, avoids laminating the bad pressure that produces among the optical cement layer process and harms the reflecting layer, consequently, the display substrate of this disclosure embodiment has promoted rear end module laminating and reliability yield by a wide margin.

Additional features and advantages of the disclosure will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by the practice of the disclosure. The objects and advantages of the disclosure may be realized and attained by the structure particularly pointed out in the written description and drawings.

Drawings

The accompanying drawings are included to provide a further understanding of the disclosed embodiments and are incorporated in and constitute a part of this specification, illustrate embodiments of the disclosure and together with the example serve to explain the principles of the disclosure and not to limit the disclosure.

FIG. 1 is a schematic top view of a display substrate in an exemplary embodiment of the present disclosure;

FIG. 2 is a schematic view of the cross-sectional A-A configuration of FIG. 1 in an exemplary embodiment;

FIG. 3 is a schematic view of a cross-sectional A-A configuration of FIG. 1 in another exemplary embodiment;

FIG. 4 is a schematic cross-sectional view of a substrate after a base structure layer is formed thereon;

FIG. 5 is a schematic cross-sectional view of a substrate with a driving structure layer;

FIG. 6 is a schematic cross-sectional view of a substrate after a light-emitting structure layer is formed thereon;

FIG. 7 is a cross-sectional view of a substrate after a package structure layer is formed thereon;

FIG. 8a is a schematic cross-sectional view of a substrate with a reflective layer formed thereon;

FIG. 8b is a schematic top view of the display substrate after forming a reflective layer thereon;

FIG. 9a is a schematic cross-sectional view illustrating a substrate after a hydrophilic material layer is formed thereon;

FIG. 9b is a schematic top view illustrating a structure of the substrate after forming a hydrophilic material layer thereon;

FIG. 10 is a schematic cross-sectional view of a display substrate;

FIG. 11 is a schematic diagram of a prior art mirror display device;

fig. 12 is a schematic view of a method of manufacturing a display substrate in an exemplary embodiment of the present disclosure.

Description of reference numerals:

11-a hard carrier plate; 12-a base structure layer; 121 — a first substrate;

122 — a second substrate; 123 — a third substrate; 124-a buffer layer;

131-an active layer; 132 — a first insulating layer; 133 a-gate electrode;

133b — first pattern; 134-a second insulating layer; 135a — a second pattern;

136 — third insulating layer; 137 a-source electrode; 137b — drain electrode;

138 — fourth insulating layer; 13-driving the structural layer; 20-a light emitting structure layer;

21-a pixel defining layer; 22 — a first electrode layer; 23 — an organic light-emitting layer;

24 — a second electrode layer; 30-packaging the structural layer; 31 — a first inorganic encapsulation layer;

32-organic encapsulation layer; 33 — a second inorganic encapsulation layer; 40-a reflective layer;

41-light hole; 42-first exposure hole; 50-a layer of hydrophilic material;

52-second exposure hole; 61-optical glue layer; 62, covering plate;

70-a protective layer; 100-a display area; 200-a frame region;

300-binding region.

Detailed Description

To make the objects, technical solutions and advantages of the present disclosure more apparent, embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings. Embodiments may be embodied in many different forms. Those skilled in the art can readily appreciate the fact that the forms and details may be varied into a variety of forms without departing from the spirit and scope of the present disclosure. Therefore, the present disclosure should not be construed as being limited to the contents described in the following embodiments. The embodiments and features of the embodiments in the present disclosure may be arbitrarily combined with each other without conflict.

In the drawings, the size of each component, the thickness of layers, or regions may be exaggerated for clarity. Therefore, the embodiments of the present disclosure are not necessarily limited to the dimensions, and the shapes and sizes of the respective components in the drawings do not reflect a true scale. Further, the drawings schematically show ideal examples, and the embodiments of the present disclosure are not limited to the shapes or numerical values shown in the drawings.

The ordinal numbers such as "first", "second", "third", and the like in the present specification are provided for avoiding confusion among the constituent elements, and are not limited in number.

In this specification, for convenience, words such as "middle", "upper", "lower", "front", "rear", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicating orientations or positional relationships are used to explain positional relationships of constituent elements with reference to the drawings, only for convenience of description and simplification of description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed in a specific orientation, and be operated, and thus, should not be construed as limiting the present disclosure. The positional relationship of the components is changed as appropriate in accordance with the direction in which each component is described. Therefore, the words described in the specification are not limited to the words described in the specification, and may be replaced as appropriate.

In this specification, the terms "mounted," "connected," and "connected" are to be construed broadly unless otherwise specifically indicated and limited. For example, it may be a fixed connection, or a removable connection, or an integral connection; can be a mechanical connection, or an electrical connection; either directly or indirectly through intervening components, or both may be interconnected. The specific meaning of the above terms in the present disclosure can be understood in specific instances by those of ordinary skill in the art.

In this specification, a transistor refers to an element including at least three terminals, i.e., a gate electrode, a drain electrode, and a source electrode. The transistor has a channel region between a drain electrode (drain electrode terminal, drain region, or drain electrode) and a source electrode (source electrode terminal, source region, or source electrode), and current can flow through the drain electrode, the channel region, and the source electrode. In this specification, the channel region refers to a region through which current mainly flows.

In this specification, the first electrode may be a drain electrode and the second electrode may be a source electrode, or the first electrode may be a source electrode and the second electrode may be a drain electrode. In the case of using transistors of opposite polarities, or in the case of changing the direction of current flow during circuit operation, the functions of the "source electrode" and the "drain electrode" may be interchanged. Therefore, in this specification, "source electrode" and "drain electrode" may be exchanged with each other.

In this specification, "electrically connected" includes a case where constituent elements are connected together by an element having some kind of electrical action. The "element having a certain electric function" is not particularly limited as long as it can transmit and receive an electric signal between connected components. Examples of the "element having some kind of electric function" include not only an electrode and a wiring but also a switching element such as a transistor, a resistor, an inductor, a capacitor, other elements having various functions, and the like.

In the present specification, "parallel" means a state in which an angle formed by two straight lines is-10 ° or more and 10 ° or less, and therefore, includes a state in which the angle is-5 ° or more and 5 ° or less. The term "perpendicular" refers to a state in which the angle formed by two straight lines is 80 ° or more and 100 ° or less, and therefore includes a state in which the angle is 85 ° or more and 95 ° or less.

Fig. 10 is a schematic cross-sectional view of a display substrate. As shown in fig. 10, the display substrate includes a substrate 10, a light emitting structure layer 20, and an encapsulation structure layer 30. The light emitting structure layer 20 is positioned at one side of the base substrate 10, and the light emitting structure layer 20 includes a plurality of light emitting cells 201. The package structure layer 30 is located at a side of the light emitting structure layer 20 facing away from the substrate base plate 10. The display substrate further comprises a reflective layer 40, an optical glue layer 61 and a cover plate 62. The reflective layer 40 is located on one side of the package structure layer 30 departing from the substrate base plate 10, the optical adhesive layer 61 is attached to one side of the reflective layer 40 departing from the substrate base plate 10, and the cover plate 62 is attached to the optical adhesive layer 61.

The light emitting unit emits light to perform display, and external light is reflected by the reflective layer 40 after irradiating the reflective layer 40, so that the display substrate shown in fig. 10 is a mirror display substrate and has functions of both display and mirror.

When the display substrate shown in fig. 10 is formed, the optical adhesive layer 61 is directly attached to the upper side of the emission layer 40. When a bonding press failure occurs in the process of bonding the optical adhesive layer 61, the reflective layer 40 may be damaged or defects such as bubbles and detachment may occur, which may result in a decrease in the product reliability yield.

Fig. 1 is a schematic top view structure of a display substrate in an exemplary embodiment of the disclosure, fig. 2 is a schematic a-a cross-sectional structure of fig. 1 in an exemplary embodiment, and fig. 2 illustrates only one light emitting unit and one thin film transistor as an example. The present disclosure provides a display substrate, as shown in fig. 1 and 2, the display substrate includes a display area 100, a bezel area 200 located at the periphery of the display area 100, and a binding area 300. The display substrate includes a substrate 10, a light emitting structure layer 20, and an encapsulation structure layer 30. The light emitting structure layer 20 is positioned at one side of the substrate 10, and the light emitting structure layer 20 includes a plurality of light emitting cells 201 positioned in the display region 100. The package structure layer 30 is located at a side of the light emitting structure layer 20 facing away from the substrate base plate 10. The display substrate further comprises a reflective layer 40, wherein the reflective layer 40 is located on a side of the package structure layer 30 facing away from the substrate 10. The display substrate further comprises a layer of hydrophilic material 50, an optical glue layer 61 and a cover plate 62. The hydrophilic material layer 50 is located on the side of the reflection layer 40 facing away from the substrate base plate 10, the optical adhesive layer 61 is located on the side of the hydrophilic material layer 50 facing away from the substrate base plate 10, and the cover plate 62 is located on the side of the optical adhesive layer 61 facing away from the substrate base plate 10.

In the display substrate of the embodiment of the disclosure, the hydrophilic material layer 50 is arranged on the side of the reflective layer 40 departing from the substrate 10, and the optical adhesive layer 61 is attached to the surface of the hydrophilic material layer 50, compared with the case that the optical adhesive layer 61 is directly attached to the reflective layer 40, the hydrophilic material layer 50 can improve the adhesion of the optical adhesive layer 61 to the surface of the hydrophilic material layer 50, and avoid the defects of bubbles, separation and the like between the interface of the optical adhesive layer 61 and the interface of the hydrophilic material layer 50; in addition, the hydrophilic material layer 50 can protect the reflective layer 40, and the reflective layer is prevented from being damaged by bad pressing generated in the process of attaching the optical adhesive layer 61, so that the attachment and reliability yield of the rear-end module is greatly improved for the display substrate of the embodiment of the disclosure.

In an exemplary embodiment, the material of the hydrophilic material layer 50 may be a silicon-based super hydrophilic oxide, such as silicon dioxide (SiO)₂) It may also be Organic Colloids (OC) having hydrophilicity, such as transparent photoresist, etc. In one exemplary embodiment, the thickness of the hydrophilic material layer may be 1200 angstroms to 1700 angstroms, such as 1200 angstroms, 1300 angstroms, 1400 angstroms, 1500, 1600 angstroms, or 1700 angstroms.

In an exemplary embodiment, the reflective layer 40 is formed with light holes 41 corresponding to the light emitting units 201 one by one, and the reflective layer 40 is further formed with first exposure holes 42 located in the bonding region, wherein the first exposure holes 42 are used for exposing the bonding pads so as to be bonded and connected with the driver IC and the flexible circuit board.

FIG. 11 is a schematic diagram of a prior art mirror display device. In the prior art, as shown in fig. 11, a mirror display device includes a display substrate 80 and a transflective film 81 located on a light-emitting side of the display substrate 80. The light displayed on the display substrate is transmitted through the transflective film 81 to be displayed, and the external light is irradiated onto the transflective film 81 and then reflected, thereby achieving the effects of display and mirror. However, the semi-transparent and semi-reflective film reduces the transmittance of the display device, and a portion of the external light transmits through the semi-transparent and semi-reflective film, so that the display contrast of the mirror display device is low due to the influence of the external light on the light displayed on the display substrate.

In the display substrate in the embodiment of the present disclosure, the light holes 41 corresponding to the light emitting units 201 one to one are formed in the reflective layer 40, so that the light emitted by the light emitting units 201 can be emitted through the light holes 41, the display transmittance of the display device is improved, and the light emitted by the light emitting units 201 is no longer affected by external light, thereby improving the display contrast of the display device. Meanwhile, at the non-light emitting unit position of the display area, the external light irradiates the reflective layer 40 and is reflected, thereby realizing the function of a mirror.

Fig. 3 is a schematic view of a-a cross-sectional structure of fig. 1 in another exemplary embodiment, and fig. 3 illustrates only one light emitting unit and one thin film transistor as an example. In one exemplary embodiment, as shown in fig. 3, the display substrate may further include a protective layer 70 between the encapsulation structure layer 30 and the reflective layer 40. In an exemplary embodiment, the material of the protection layer 70 may be silicon nitride SiNx, silicon oxide SiOx, or a composite layer of SiNx/SiOx. In one exemplary embodiment, the material of the protective layer 70 is SiNx. The thickness of the protective layer 70 may be 0.2 μm to 0.4 μm, for example, the thickness of the protective layer 70 may be 0.3 μm.

In one exemplary embodiment, as shown in fig. 2 or 3, the substrate base plate 10 may include a base structure layer 12 and a driving structure layer 13 positioned at a side of the base structure layer 12 facing the light emitting structure layer 20. In one exemplary embodiment, the base structure layer 12 may include a first substrate 121, a second substrate 122, a third substrate 123, and a buffer layer 124 sequentially stacked, the buffer layer 124 facing the driving structure layer 13. In one exemplary embodiment, the base structure layer 12 may include a first substrate 121, a second substrate 122, and a buffer layer 124 sequentially stacked, with the buffer layer 124 facing the driving structure layer 13.

In an exemplary embodiment, the first substrate, the second substrate, and the third substrate may be made of a Pressure Sensitive Adhesive (PSA), Polyimide (PI), polyethylene terephthalate (PET), or a surface-treated polymer film. In an exemplary embodiment, the material of the first substrate 121 is a pressure sensitive adhesive, and the material of the second substrate 122 and the third substrate 123 are polyimide. The buffer layer 124 may be made of silicon nitride SiNx, silicon oxide SiOx, or a composite layer of SiNx/SiOx.

In one exemplary embodiment, the driving structure layer 13 may include thin film transistors, as shown in fig. 3, and only one thin film transistor 201 is shown in fig. 3.

In an exemplary embodiment, as shown in fig. 1, the display substrate includes a plurality of pixel units 400 located in the display area 100, and the plurality of pixel units 400 are arranged in an array. Each pixel unit 400 includes a plurality of light emitting units. In one exemplary embodiment, the light emitting unit is an OLED light emitting unit, and the light emitting unit may include an anode, an organic light emitting layer, and a cathode.

In one exemplary embodiment, the pixel unit 400 includes a first light emitting unit 401, a second light emitting unit 402, and a third light emitting unit 403. The three light emitting units may be arranged in an array, and each light emitting unit has a rectangular structure, as shown in fig. 1. It should be understood by those skilled in the art that the arrangement of the three light emitting units, the structure and the size of each light emitting unit can be determined according to actual needs, and are not limited herein. In one exemplary embodiment, the first light emitting unit 401 may be configured as a red light emitting unit, the second light emitting unit 402 may be configured as a green light emitting unit, and the third light emitting unit 403 may be configured as a blue light emitting unit. Those skilled in the art will appreciate that the color of each light emitting unit in the pixel unit 400 can be determined according to actual needs, and is not limited herein.

In an exemplary embodiment, the number of the light emitting units in the pixel unit 400 may also be 4 or more, which is not limited herein. The arrangement of the plurality of light emitting units, the shape, size, and color of each light emitting unit can be determined according to actual needs, and are not limited herein.

In one exemplary embodiment, each light emitting unit may employ the same organic light emitting layer, and thus, each light emitting unit emits light of the same color, for example, white light. The light with the required color, such as white light and a red color film, can be obtained by combining the light-emitting unit with the color film to obtain a red light-emitting unit; white light and a blue color film to obtain a blue light-emitting unit; white light and a green color film to obtain a green light emitting unit.

In an exemplary embodiment, the organic light emitting layers may be configured to emit red light, green light, and blue light, respectively, so that the light emitting units may be a red light emitting unit, a green light emitting unit, and a blue light emitting unit, respectively, and light emission is not assisted by a color film.

In one exemplary embodiment, as shown in fig. 2 or 3, the substrate base plate 10 may include a base structure layer 12 and a driving structure layer 13. The driving structure layer 13 is located on a side of the base structure layer facing the light emitting structure layer 20. The substrate structure layer 12 includes a first substrate, a second substrate, a third substrate and a buffer layer sequentially stacked. The driving structure layer 13 is located on a side of the buffer layer facing away from the first substrate. In one exemplary embodiment, the first, second, and third substrates each comprise at least one of the following materials: pressure sensitive adhesive, polyimide, polyethylene terephthalate, and surface-treated polymer film.

In one exemplary embodiment, the display substrate of the embodiments of the present disclosure is a flexible OLED mirror display substrate, combining the functions of a display and a mirror.

The structure of the display substrate of the embodiments of the present disclosure is explained below through the process of manufacturing the display substrate. For describing the mask number of the display substrate in detail, the "patterning process" is used hereinafter to refer to a process of forming a patterning each time, each patterning process corresponds to a mask process, and for an inorganic material (e.g., a metal layer, an inorganic layer, etc.), the "patterning process" may include processes of coating a photoresist, mask exposure, developing, etching, and stripping the photoresist; for organic materials (e.g., photoresist, organic resin, etc.), the "patterning process" may include a mask exposure, development process. The deposition may employ any one or more of sputtering, evaporation and chemical vapor deposition, the coating may employ any one or more of spray coating and spin coating, and the etching may employ any one or more of dry etching and wet etching. "thin film" refers to a layer of a material deposited or coated onto a substrate. The "thin film" may also be referred to as a "layer" if it does not require a patterning process throughout the fabrication process. If the "thin film" requires a patterning process during the entire fabrication process, it is referred to as a "thin film" before the patterning process and a "layer" after the patterning process. The "layer" after the patterning process includes at least one "pattern". The "a and B are disposed in the same layer" in the present disclosure means that a and B are simultaneously formed by the same patterning process. The "thickness" of a film layer is the dimension of the film layer in the direction perpendicular to the substrate.

(1) A base structure layer 12 is formed. This step may include: coating a first flexible material on the hard carrier plate 11, and curing to form a film to form a first substrate 121; coating a second flexible material on the side of the first substrate 121 away from the hard carrier 11, and curing to form a film, so as to form a second substrate 122; coating a third flexible material on one side of the second substrate 122, which is far away from the hard carrier 11, and curing to form a film to form a third substrate 123; as shown in fig. 4, a buffer film is deposited on a side of the third substrate 133 away from the hard carrier 11 to form a buffer layer 124, and fig. 4 is a schematic cross-sectional structure diagram after a substrate structure layer is formed in the display substrate. As shown in fig. 4, the formed substrate structure layer includes a first substrate 121, a second substrate 122, a third substrate 123 and a buffer layer 124 sequentially stacked on the hard carrier 11.

In an exemplary embodiment, the substrate structure layer 12 may include a first substrate 121, a second substrate 122, and a buffer layer 124 sequentially stacked on the rigid carrier 11. In an exemplary embodiment, each of the first flexible material, the second flexible material and the third flexible material may be at least one of a Pressure Sensitive Adhesive (PSA), a Polyimide (PI), a polyethylene terephthalate (PET) or a surface-treated polymer film. The first flexible material, the second flexible material and the third flexible material may be the same material or different materials. In an exemplary embodiment, the material of the first substrate 121 is a pressure sensitive adhesive, and the material of the second substrate 122 and the third substrate 123 are polyimide. The buffer layer 124 may be made of silicon nitride SiNx, silicon oxide SiOx, or a composite layer of SiNx/SiOx.

In the process of forming the base structure layer 12, no patterning process is used, and no patterning process is used.

(2) As shown in fig. 5, a driving structure layer is formed on the base structure layer 12, and fig. 5 is a schematic cross-sectional structure diagram of the display substrate after the driving structure layer is formed. The driving structure layer comprises a thin film transistor. Forming the driving structure layer may include:

the first patterning process: an active layer 131 is formed on the base structure layer 12, and the active layer 131 is located in the display region. This step may include: an active film is deposited on the side of the buffer layer 124 away from the hard carrier 11, and the active film is patterned through a patterning process to form an active layer 131, as shown in fig. 5. In an exemplary embodiment, the material of the active thin film may also be Low Temperature Polysilicon (LTPS) or microcrystalline Silicon material, and may also be a metal Oxide material, which may be Indium Gallium Zinc Oxide (IGZO) or Indium Tin Zinc Oxide (ITZO).

And (3) a second patterning process: a first metal layer is formed on the side of the active layer 131 facing away from the base structure layer 12. This step may include: depositing a first insulating film on the side of the active layer 131 away from the base structure layer to form a first insulating layer 132; a first metal film is deposited on a side of the first insulating layer 132 away from the substrate structure layer, and is patterned by a patterning process to form a first metal layer, where the first metal layer includes a gate electrode 133a, a first pattern 133b, and a gate line (not shown), and the gate electrode 133a and the first pattern 133b are both located in the display region. In one exemplary embodiment, the first metal thin film may employ one or more of platinum Pt, ruthenium Ru, gold Au, silver Ag, molybdenum Mo, chromium Cr, aluminum Al, tantalum Ta, titanium Ti, tungsten W, and the like. The first insulating film may be silicon nitride SiNx, silicon oxide SiOx, or a composite layer of SiNx/SiOx.

And (3) a third patterning process: a second metal layer is formed on the side of the first metal layer facing away from the base structure layer 12. This step may include: depositing a second insulating film on the side of the first metal layer away from the base structure layer 12 to form a second insulating layer 134; a second metal film is deposited on the side of the second insulating layer 134 facing away from the base structure layer 12, and is patterned by a patterning process to form a second metal layer, which includes a second pattern 135a in the display region, as shown in fig. 5. The second pattern 135a corresponds to the first pattern 133b, and the second pattern 135a and the first pattern 133b form two plates of a capacitor. In one exemplary embodiment, the second metal thin film may employ one or more of platinum Pt, ruthenium Ru, gold Au, silver Ag, molybdenum Mo, chromium Cr, aluminum Al, tantalum Ta, titanium Ti, tungsten W, and the like. The second insulating film may be silicon nitride SiNx, silicon oxide SiOx, or a composite layer of SiNx/SiOx.

Fourth patterning: a third insulating layer 136 is formed on a side of the second metal layer 135 away from the base structure layer 12, and the third insulating layer 136 is provided with a first via hole and a second via hole penetrating through the third insulating layer 136, the second insulating layer 134 and the first insulating layer 132, where the first via hole is used to expose one end of the active layer 131, and the second via hole is used to expose the other end of the active layer 131. This step may include: a third insulating film is deposited on a side of the second metal layer 135 away from the base structure layer 12, and the third insulating film, the second insulating layer 134 and the first insulating layer 132 are patterned by a patterning process to form a first via hole and a second via hole, wherein the first via hole exposes one end of the active layer 131, and the second via hole exposes the other end of the active layer 131, as shown in fig. 5. In one exemplary embodiment, the third insulating film may employ silicon nitride SiNx, silicon oxide SiOx, or a composite layer of SiNx/SiOx.

And a fifth patterning process: and forming a third metal layer on the side of the third insulating layer 136 away from the base structure layer 12, where the third metal layer includes a source electrode 137a and a drain electrode 137b, the source electrode 137a is connected with one end of the active layer 131 through a first via hole, the drain electrode 137b is connected with the other end of the active layer 131 through a second via hole, and the source electrode 137a and the drain electrode 137b are both located in the display region. This step may include: depositing a third metal film on the side of the third insulating layer 136 away from the substrate structure layer 12, and patterning the third metal film through a patterning process to form a third metal layer, where the third metal layer includes a source electrode 137a, a drain electrode 137b and a data line (not shown in the figure) located in the display region, the source electrode 137a is connected to one end of the active layer 131 through a first via hole, and the drain electrode 137b is connected to the other end of the active layer 131 through a second via hole.

(3) A light emitting structure layer is formed on a side of the driving structure layer away from the base structure layer 12, as shown in fig. 6, and fig. 6 is a schematic cross-sectional structure diagram after the light emitting structure layer is formed in the display substrate. The light emitting structure layer includes a plurality of light emitting cells 201 in the display region 100, and the light emitting cells include a first electrode pattern, an organic light emitting layer, and a second electrode layer. Forming the light emitting structure layer may include:

and a sixth patterning process: a fourth insulating layer 138 is formed on a side of the driving structure layer facing away from the base structure layer 12, and the fourth insulating layer 138 is provided with a third via hole for exposing the drain electrode 137 b. This step may include: a fourth insulating film is coated on the side of the driving structure layer away from the base structure layer 12, the fourth insulating film is patterned by a patterning process to form a fourth insulating layer 138, the fourth insulating layer 138 is provided with a third via hole, and the drain electrode 137b is exposed through the third via hole, as shown in fig. 6. In an exemplary embodiment, a material of the fourth insulating layer is an organic material, such as a photoresist, a resin material, and the like. The surface of the fourth insulating layer, which is away from one side of the base structure layer, is a flat surface.

And a seventh patterning process: the first electrode layer 22 is formed on a side of the fourth insulating layer 138 away from the base structure layer 12, and the first electrode layer 22 includes a first electrode pattern 22a located in a region where the light emitting unit is located. This step may include: depositing a first conductive film on a side of the fourth insulating layer 138 away from the substrate structure layer 12, patterning the first conductive film through a patterning process to form the first electrode layer 22, where the first electrode layer 22 includes a plurality of first electrode patterns 22a, the first electrode patterns 22a are located in a region where the light emitting unit is located, and the first electrode patterns 22a are connected to the drain electrode 137b through third via holes, as shown in fig. 6. The first conductive film may be made of a material commonly used in the art, such as Indium Tin Oxide (ITO), Indium Zinc Oxide (IZO), or ITO/Al (aluminum)/ITO multilayer composite material, and is not particularly limited herein. The first electrode pattern 22a may be an anode of the OLED light emitting unit.

And an eighth patterning process: a pixel defining layer 21 is formed on a side of the first electrode layer 22 away from the substrate structure layer 12, a pixel opening is formed in a region where each light emitting unit is located in the pixel defining layer 22, and the first electrode pattern 22a is exposed through the pixel opening. This step may include: a pixel defining film is formed on a side of the first electrode layer 22 away from the substrate structure layer 12, and is patterned by a patterning process to form a pixel defining layer 21, a pixel opening is formed in a region where each light emitting unit is located on the pixel defining layer 22, and the first electrode pattern 22a is exposed through the pixel opening, as shown in fig. 6. In one exemplary embodiment, the pixel defining layer may be made of polyimide, acryl, or polyethylene terephthalate.

An organic light-emitting material and a second conductive material are sequentially deposited on the side of the first electrode layer 22 facing away from the base structure layer 12 to form an organic light-emitting layer 23 and a second electrode layer 24. The organic light emitting layer 23 is connected to the first electrode pattern 22a, and the second electrode layer 24 is located on a surface of the organic light emitting layer 23 facing away from the base structure layer 12, as shown in fig. 6. The organic light emitting layer 23 mainly includes an emission layer (EML). The organic light emitting layer may include a hole injection layer, a hole transport layer, a light emitting layer, an electron transport layer, and an electron injection layer, which are sequentially disposed. In order to improve efficiency of electron and hole injection into the light emitting layer, one or more of metal materials such as magnesium (Mg), silver (Ag), aluminum (Al), copper (Cu), lithium (Li), and the like may be used as the second conductive material. The second electrode layer may be a cathode of the light emitting unit, and the cathodes of all the light emitting units are of an integral structure.

As will be understood by those skilled in the art, the forming of the light emitting structure layer further includes a ninth patterning process, in which the spacers (PS) are formed in the frame region.

(4) As shown in fig. 7, an encapsulation structure layer 30 is formed on a side of the light emitting structure layer 20 away from the base structure layer 12, and fig. 7 is a schematic cross-sectional structure diagram after the encapsulation structure layer is formed in the display substrate. The encapsulation structure layer 30 includes a first inorganic encapsulation layer 31, an organic encapsulation layer 32 and a second inorganic encapsulation layer 33, the orthographic projections of the first inorganic encapsulation layer 31, the organic encapsulation layer 32 and the second inorganic encapsulation layer 33 on the base structure layer 12 all include a display area, in an exemplary embodiment, the first inorganic encapsulation layer 31 and the second inorganic encapsulation layer 33 are located in the display area and the frame area, and the organic encapsulation layer 32 is located in the display area. The process of forming the package structure layer 30 may include:

the first inorganic encapsulation layer 31 is formed at a side of the light emitting structure layer 20 facing away from the base structure layer 12. This step may include: depositing a first inorganic encapsulation film on the side of the light emitting structure layer 20 away from the base structure layer 12 to form a first inorganic encapsulation layer 31, wherein the first inorganic encapsulation layer 31 is located in the display area and the frame area. In one exemplary embodiment, the first inorganic encapsulation film may employ silicon nitride SiNx, silicon oxide SiOx, or a composite layer of SiNx/SiOx. In one exemplary embodiment, the first inorganic encapsulation film employs silicon oxynitride SiON.

An organic encapsulation layer 32 is formed on the side of the first inorganic encapsulation layer 31 facing away from the base structure layer 12. This step may include: and ink-jet printing the organic packaging material on the side of the first inorganic packaging layer 31, which is far away from the substrate structure layer 12, by adopting an ink-jet printing process, curing to form a film, and forming an inorganic packaging layer 32, wherein the inorganic packaging layer 32 can be ink-jet printed in the display area only.

A second inorganic encapsulation layer 33 is formed on the side of the organic encapsulation layer 32 facing away from the base structure layer 12. This step may include: and depositing a second inorganic packaging film on the side of the organic packaging layer 32, which is far away from the base structure layer 12, to form a second inorganic packaging layer 33, wherein the second inorganic packaging layer 33 is positioned in the display area and the frame area. In one exemplary embodiment, the second inorganic encapsulation film may employ silicon nitride SiNx, silicon oxide SiOx, or a composite layer of SiNx/SiOx. In one exemplary embodiment, the first inorganic encapsulation film employs silicon nitride SiNx.

In one exemplary embodiment, the thickness of the first inorganic encapsulation layer 31 may be 1 μm, the thickness of the organic encapsulation layer 32 may be 12 μm, and the thickness of the second inorganic encapsulation layer 33 may be 500nm to 700nm (e.g., 600 nm).

(5) The tenth patterning process: a reflective layer 40 is formed on a side of the package structure layer 30 away from the base structure layer 12, the reflective layer 40 is formed with light holes 41 corresponding to the light emitting units one by one, the reflective layer 40 is further formed with first exposure holes 42, the first exposure holes 42 are located in the bonding regions, and the first exposure holes are used for exposing the bonding pads so as to be bonded and connected with the driver IC and the flexible circuit board, as shown in fig. 8a and 8b, fig. 8a is a schematic cross-sectional structure diagram after the reflective layer is formed in the display substrate, and fig. 8b is a schematic top view structure diagram after the reflective layer is formed in the display substrate. This step may include: depositing a reflective film on a side of the package structure layer 30 away from the base structure layer 12, and patterning the reflective film through a patterning process to form light-transmitting holes 41 corresponding to the light-emitting units one by one and first exposed holes in the bonding region. The light emitted from the light emitting unit can exit through the light transmission hole 41, and the first exposure hole is used for exposing the bonding pad so as to be bonded and connected with the driver IC and the flexible circuit board.

In one exemplary embodiment, the area of all the light transmission holes 41 on the reflective layer 40 accounts for 10% to 40% of the display area of the display substrate, i.e., the area of the orthographic projection of the reflective layer 40 on the plane parallel to the display substrate is 60% to 90% of the display area of the display substrate. The area of the light hole 41 and the area of the light emitting unit (it is understood that, since the light emitting unit includes a plurality of film layers, the area of the light emitting unit is the area of the orthographic projection of the light emitting unit on the substrate structure layer, and the area of the pixel opening corresponding to the light emitting unit) are not limited, and the area of the light hole 41 may be larger than, smaller than, or equal to the area of the light emitting unit. The mirror effect is reduced by the area of the light-transmitting hole 41, but the brightness of the display substrate is improved, and the mirror effect is enhanced by the area of the light-transmitting hole 41, but the brightness of the display substrate is reduced. The shape of the light-transmitting hole 41 is not limited herein, and may be square, circular, a shape conforming to the light-emitting unit, or the like according to actual needs.

In one exemplary embodiment, the orthographic projection of the reflective layer on the base structure layer covers all areas of the display area of the display substrate except for the light emitting units, i.e., exposes all the light emitting units.

In one exemplary embodiment, the material of the reflective layer may include one or more of Molybdenum (MO), aluminum (Al), silver (Ag), titanium (Ti), ITO/Ag/ITO multilayer composite, Ti/Al/Ti multilayer composite. In one exemplary embodiment, the reflective layer may have a thickness of 0.25 μm to 0.4 μm. In one exemplary embodiment, the material of the reflective layer is aluminum with a thickness of 0.33 μm.

In an exemplary embodiment, the orthographic projection of the reflective layer 40 on the substrate includes the orthographic projection of the package structure layer 30 on the substrate, so that the package structure layers 30 are all covered by the reflective layer 40, and the mirror effect is improved.

(6) An eleventh patterning process: a hydrophilic material layer 50 is formed on a side of the reflective layer 40 away from the substrate structure layer 12, the hydrophilic material layer 50 is provided with a second exposure hole 52, the second exposure hole 52 is located in the bonding region, the second exposure hole 52 is used for exposing the bonding pad so as to be bonded with the driver IC and the flexible circuit board, as shown in fig. 9a and 9b, fig. 9a is a schematic diagram illustrating a cross-sectional structure after the hydrophilic material layer is formed in the substrate, and fig. 9b is a schematic diagram illustrating a top view structure after the hydrophilic material layer is formed in the substrate. This step may include: forming a hydrophilic material film on the side of the reflective layer 40 away from the base structure layer 12, and patterning the hydrophilic material film through a patterning process to form a hydrophilic material layer 50, wherein the hydrophilic material layer 50 is provided with second exposure holes 52 located in the bonding areas, and the second exposure holes 52 are used for exposing the bonding pads so as to be bonded and connected with the driver IC and the flexible circuit board, as shown in fig. 8a and 8 b. It will be understood by those skilled in the art that during the formation of the second exposure holes 52, the materials of the corresponding positions of the first inorganic encapsulation layer and the second inorganic encapsulation layer are simultaneously removed, so that the bonding pads can be exposed through the second exposure holes.

In one exemplary embodiment, the hydrophilic material layer may employ a silicon-based super hydrophilic oxide, such as silicon dioxide (SiO)₂) Organic Colloids (OC) having hydrophilicity, such as transparent photoresist, and the like, can also be used. In one exemplary embodiment, the thickness of the hydrophilic material layer may be 1200 to 1700 angstroms, for example 1500 angstroms.

In an exemplary embodiment, the orthographic projection of the hydrophilic material layer 50 on the substrate includes the orthographic projection of the reflective layer on the substrate, that is, the hydrophilic material layer covers the reflective layer, so that the hydrophilic material layer can protect the entire reflective layer and prevent the reflective layer from being damaged by bad pressing generated during the process of attaching the optical adhesive layer 61.

(7) An optical adhesive layer 61 is attached to the side of the hydrophilic material layer 50 away from the base structure layer 12 by an attaching process, as shown in fig. 2.

Because the optical adhesive layer 61 is attached to the surface of the hydrophilic material layer 50, compared with attaching the optical adhesive layer 61 to the reflective layer 40, the hydrophilic material layer 50 can improve the adhesion of the optical adhesive layer 61 to the surface of the hydrophilic material layer 50, and avoid the generation of bubbles, separation and other defects between the interface of the optical adhesive layer 61 and the hydrophilic material layer 50; in addition, the hydrophilic material layer 50 can protect the reflective layer 40, prevent the reflective layer from being damaged by bad pressing generated in the process of attaching the optical adhesive layer 61, and greatly improve the attachment and reliability yield of the rear-end module.

Subsequently, a cover plate 62 is attached to the side of the optical adhesive layer 61 away from the base structure layer by using an attaching process.

In one exemplary embodiment, the thickness of the optical glue layer may be 40 μm to 60 μm, for example, 50 μm. The thickness of the cover plate may be 50 μm to 70 μm, for example 60 μm.

It will be understood by those skilled in the art that, in the preparation of the flexible display substrate, the preparation process of the display substrate further includes peeling off the rigid carrier 11, and the rigid carrier 11 may be peeled off by using processes and methods known in the art, which are not limited herein.

In one exemplary embodiment, the process of preparing the display substrate may further include: a protective layer 70 is formed between the encapsulation structure layer 30 and the reflective layer 40. This step may include: a protective film is formed on one side of the package structure layer 30 facing the reflective layer 40, and is patterned by a patterning process to form a protective layer 70, where the protective layer 70 is provided with a third exposure hole, the third exposure hole is located in the bonding region, and the third exposure hole is used for exposing the bonding pad so as to be bonded and connected with the driver IC and the flexible circuit board, as shown in fig. 3. Since the protective layer 70 is patterned, a mask process is also required to form the protective layer. In an exemplary embodiment, the material of the protection layer 70 may be silicon nitride SiNx, silicon oxide SiOx, or a composite layer of SiNx/SiOx. In one exemplary embodiment, the material of the protective layer 70 is SiNx. The thickness of the protective layer 70 may be 0.2 μm to 0.4 μm, for example, the thickness of the protective layer 70 may be 0.2 μm, 0.3 μm, or 0.4 μm.

In one exemplary embodiment, the orthographic projection of the protective layer 70 on the substrate includes the orthographic projection of the package structure layer 30 on the substrate. Therefore, during the reflective layer patterning process, the protection layer 70 can protect the entire package structure layer and prevent the package structure layer from being etched.

An embodiment of the present disclosure further provides a method for manufacturing a display substrate, fig. 12 is a schematic diagram of a method for manufacturing a display substrate according to an exemplary embodiment of the present disclosure, and as shown in fig. 12, the method for manufacturing a display substrate may include:

In one exemplary embodiment, the display substrate includes a display region, a frame region located at a periphery of the display region, and a binding region, and a hydrophilic material layer is formed on a side of the reflective layer facing away from the substrate, including:

The detailed manufacturing process of the display substrate has been described above and will not be described herein.

Based on the inventive concept of the foregoing embodiments, embodiments of the present disclosure also provide a display device, which includes the display substrate employing the foregoing embodiments, and the display device may be a flexible OLED mirror display device. The display device may be: any product or component with a display function, such as a mobile phone, a tablet computer, a television, a display, a notebook computer, a digital photo frame, a navigator and the like.

Although the embodiments disclosed in the present disclosure are described above, the descriptions are only for the convenience of understanding the present disclosure, and are not intended to limit the present disclosure. It will be understood by those skilled in the art of the present disclosure that various changes in form and details may be made therein without departing from the spirit and scope of the disclosure, and that the scope of the disclosure is to be limited only by the terms of the appended claims.

Claims

1. A display substrate, comprising:

a substrate base plate;

2. The display substrate according to claim 1, wherein the hydrophilic material layer comprises a silicon-based super-hydrophilic oxide, or the hydrophilic material layer comprises a hydrophilic organic colloid.

3. The display substrate of claim 1, wherein the thickness of the hydrophilic material layer is 1200 to 1700 angstroms.

4. The display substrate according to claim 1, wherein the display substrate comprises a display area, a frame area located at the periphery of the display area, and a bonding area, the hydrophilic material layer is located at the display area, the frame area, and the bonding area, and the hydrophilic material layer is provided with a second exposure hole located at the bonding area and used for exposing a bonding pad of the bonding area.

5. The display substrate of claim 4, wherein the orthographic projection of the hydrophilic material layer on the substrate comprises the orthographic projection of the reflective layer on the substrate, and the orthographic projection of the reflective layer on the substrate comprises the orthographic projection of the encapsulation structure layer on the substrate.

6. The display substrate of claim 1, wherein the reflective layer is disposed in the display region, the frame region and the bonding region, the reflective layer has light holes corresponding to the light emitting units in the display region, and the reflective layer further has first exposing holes disposed in the bonding region for exposing bonding pads of the bonding region.

7. The display substrate of claim 1, wherein the material of the reflective layer comprises one or more of the following materials: molybdenum, aluminum, silver, titanium, indium tin oxide/silver/indium tin oxide multilayer composite material, titanium/aluminum/titanium multilayer composite material.

8. The display substrate of claim 1, wherein the reflective layer has a thickness of 0.25 μm to 0.4 μm.

9. The display substrate of any one of claims 1 to 8, further comprising a protective layer between the encapsulation structure layer and the reflective layer, wherein the material of the protective layer comprises at least one of the following materials: silicon nitride, silicon oxide, and a silicon nitride/silicon oxide composite layer.

10. The display substrate according to claim 9, wherein the protective layer has a thickness of 0.2 μm to 0.4 μm.

11. The display substrate of claim 9, wherein the orthographic projection of the protective layer on the substrate comprises the orthographic projection of the encapsulation structure layer on the substrate.

12. The display substrate of claim 9, wherein the encapsulation structure layer comprises a first inorganic encapsulation layer, an organic encapsulation layer and a second inorganic encapsulation layer sequentially stacked on a side of the light emitting structure layer facing away from the substrate.

13. The display substrate of claim 1, wherein the substrate comprises a base structure layer and a driving structure layer located on a side of the base structure layer facing the light emitting structure layer, the base structure layer comprises a first base, a second base, a third base and a buffer layer, which are sequentially stacked, the driving structure layer is located on a side of the buffer layer facing away from the first base, and each of the first base, the second base and the third base comprises at least one of the following materials: pressure sensitive adhesive, polyimide, polyethylene terephthalate, and surface-treated polymer film.

14. A display device comprising the display substrate according to any one of claims 1 to 13.

15. A method for preparing a display substrate is characterized by comprising the following steps:

16. The method of claim 15, wherein the display substrate comprises a display region, a frame region located at a periphery of the display region, and a bonding region, and the forming of the hydrophilic material layer on a side of the reflective layer facing away from the substrate comprises: